Embedded wafer level ball grid array (eWLB) is a packaging technology for integrated circuits (ICs) where the package interconnects are applied on an artificial wafer made of individual semiconductor dies (chips) and a molding compound. The semiconductor dies are embedded (overmolded) by the molding compound and therefore subjected to high processing temperatures used in the molding process. A redistribution layer is applied to a side of the eWLB wafer at which the pads of the dies are available. Electrical connections are formed between the die pads and the redistribution layer. Solder bumps are provided on the redistribution layer to enable package mounting after sawing of the eWLB wafer into individual IC packages.
Certain types of semiconductor dies can be mechanically and/or thermally damaged by the overmolding and redistribution layer processes of conventional eWLB technology. For example, MEMs (microelectromechanical systems) and SAW (surface acoustic wave) filters have mechanically sensitive surfaces which should not be overmolded to ensure proper operation. Contacting light emitting or sensing devices is difficult in eWLB technology because the electrical connections are typically implemented at the uncovered bottom side of the dies. Light emitting/sensing at the top of side of the dies is not feasible because the top side of the dies is encased by a molding compound in conventional eWLB technology, obstructing the light emitting/sensing surface of the dies. Also, the high processing temperatures employed during the overmolding and redistribution layer processes of conventional eWLB technology can damage certain temperature-sensitive dies.